High-speed optical transmission systems are being standardized along with the growth in communication demand. For example, International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Recommendation G.709 defines Optical Transport Network (OTN) technology with a transmission speed of about 2.5 to 100 Gbps.
Optical transmission in the OTN uses wavelength division multiplexing (WDM) technology to multiplex a plurality of optical signals each containing a user signal, thereby making it possible to realize large-capacity transmission. Examples of the client signals contained in the optical signals include Synchronous Digital Hierarchy (SDH) frames, Synchronous Optical NETwork (SONET) frames, and Ethernet (registered trademark) frames.
In a wavelength division multiplexing apparatus employing the WDM technology (hereinafter referred to as a “WDM apparatus”), optical transceivers called transponders or the like are provided for respective communication channels, and optical signals are input and output via the respective optical transceivers. Each WDM apparatus transmits a wavelength multiplexed optical signal (hereinafter referred to as a “multiplexed optical signal”) obtained by multiplexing an optical signal input from the optical transceiver, together with an optical signal from another node, and transmits the multiplexed optical signal to another apparatus. Such an input of an optical signal from the optical transceiver is referred to as “insertion”.
Also, the WDM apparatus demultiplexes an optical signal having a predetermined wavelength from a multiplexed optical signal from another apparatus and receives the demultiplexed optical signal via an optical transceiver. Such demultiplexing of an optical signal is herein referred to as “branching”.
One example of the major costs of a network including WDM apparatuses is the number of communication channels established along paths in the network. The cost of a communication channel includes the cost of a pair of optical transceivers for performing communication through the communication channel.
Another example of the major costs is the number of WDM transmission systems. Each of the transmission systems is provided in the WDM apparatuses at a set of nodes that connect a link in the network, to transmit a wavelength multiplexing signal in which optical signals with different wavelengths are multiplexed. For example, when two optical signals with the same wavelength are transmitted through one link, at least two transmission systems are need to be provided for two opposite nodes that connect the link.
The cost of the transmission systems includes not only the cost of the transmission systems themselves but also the cost of certain floor areas in offices (that is, nodes) occupied by racks on which the transmission systems are mounted.
Thus, in network design, communication channel design and wavelength assignment design are performed based on a request for traffic between nodes. In the communication channel design, streams of traffic are assigned to communication channels so that the bandwidths of the streams of traffic are efficiently accommodated into the bandwidths of the communication channels to be established through paths in the network. In connection with the communication-channel assignment, for example, Japanese Laid-open Patent Publication No. 2013-90297 discloses a technology for performing communication channel design so that the cost of communication channels is minimized, by solving an integer programming problem.
In the wavelength assignment design, wavelengths are efficiently assigned to the communication channels so that the number of WDM systems is minimized. In connection with the wavelength assignment, for example, Japanese Laid-open Patent Publication No. 2010-199891 discloses a technology in which a preset number of routes are reserved as reserved optical paths, and reservation for assignment of routes and wavelengths is performed on each reserved optical path.